package datastructure_algorithm.queue;

public class LinkedListQueue<E> implements Queue<E> {

	private class Node {
		public E e;
		public Node next;

		public Node(E e, Node next) {
			this.e = e;
			this.next = next;
		}

		public Node(E e) {
			this(e, null);
		}

		public Node() {
			this(null, null);
		}

		@Override
		public String toString() {
			return e.toString();
		}
	}

	private Node head;
	private Node tail;
	private int size;

	public LinkedListQueue() {
		head = null;
		tail = null;
		size = 0;
	}

	@Override
	public int getSize() {
		return size;
	}

	@Override
	public boolean isEmpty() {
		return size == 0;
	}

	@Override
	public void enqueue(E e) {
		if (tail == null) { // queue is empty
			tail = new Node(e);
			head = tail;
		} else {
			tail.next = new Node(e);
			tail = tail.next;
		}
		size++;
	}

	@Override
	public E dequeue() {
		if (isEmpty()) {
			throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
		}
		Node ret = head;
		head = head.next;
//		ret.next = null; // ret will destroy when method done.
		if (head == null) {
			tail = null;
		}
		size--;
		return ret.e;
	}

	@Override
	public E getFront() {
		if (isEmpty()) {
			throw new IllegalArgumentException("Queue is empty.");
		}
		return head.e;
	}

	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();
		sb.append("LinkedListQueue: front[");
		Node cur = head;
		while (cur != null) {
			sb.append(cur + "->");
			cur = cur.next;
		}
		sb.append("null]");
		return sb.toString();
	}
	
	public static void main(String[] args) {
		LinkedListQueue<Integer> queue = new LinkedListQueue<>();
		queue.enqueue(111);
		queue.enqueue(222);
		queue.enqueue(333);
		queue.enqueue(444);
		
		queue.dequeue();
		queue.dequeue();
		queue.dequeue();
		System.out.println(queue);
	}

}
